In a radio communication system, a plurality of base stations are placed. Each base station performs communication with a radio communication user equipment (which is referred to hereinafter simply as a user equipment) in a communication area. The communication area is called a cell. Further, in order to increase the number of user equipments with which simultaneous communication is possible, an antenna may be provided with directivity, and the cell may be divided into a plurality of regions. The divided region is called a sector. In the case of using the same radio resource such as a frequency in a plurality of communication areas, there is a possibility that the communication path quality is degraded due to interference from an adjacent cell or interference from an adjacent sector. In this behalf, it is considered that the adjacent sector interference can be reduced to low enough by the directivity of the antenna.
However, at the sector boundary, because the antenna gain is equal, the communication path quality is significantly degraded due to adjacent sector interference. Further, because of shadowing in which a propagation loss varies by the effect of a building or the like, there is a case where the communication path quality is significantly degraded due to adjacent sector interference also in a user equipment not at the sector boundary.
As a technique of reducing or avoiding interference between cells that solves the above concern, a method of avoiding allocation in one's own cell or a method of reducing a transmission power depending on the frequency group allocation status in an adjacent cell or the like is known. For example, in Patent Document 1, a time-frequency group allocation method for interference reduction in an OFDMA (Orthgonal Frequency Division Multiple Access) downlink is disclosed. In Patent Document 1, a central entity that is connected to a plurality of base stations is placed, and the central entity manages scheduling of each base station. A user equipment measures a reception power of a pilot signal from each base station. The central entity performs scheduling according to the reception power reported from the user equipment in consideration of interference. Further, as an exemplary embodiment, a technique is disclosed in which frequency groups of each base station are allocated to user equipments in the area, and, for the frequency group allocated to a user equipment in a service overlap region, an adjacent base station reduces a transmission power. According to this technique, in the case of allocating a frequency group to a user equipment at the sector boundary, which is the service overlap region, for example, the same frequency group is allocated by uniformly reducing the transmission power, or the allocation of the same frequency group is avoided in an adjacent sector.